A number of polyunsaturated fatty acids (PUFA) are either essential for a normal development of the human body or potential prophylactic/ therapeutic agents for atherosclerosis, rheumatoid arthritis, carcinogenesis, type I diabetes, pre-mature birth and low birth-weight, and abnormal development of the CNS and visual acuity in new borns. 13C- Labeled PUFA are of interest for metabolic and in vivo 13C NMR studies, clinical CO2-13C breath-test for fat malabsorption, and as standards for analysis of biologic fluids. Phase I has demonstrated the steps leading to key labeled intermediates including 3-bromopropionate-1,3-13C2, 1- bromopentane-2,4-13C2, propargyl-1,3-13C2 and propargyl-2-13C alcohols. In Phase II, one additional key labeled intermediate will be prepared, and the pertinent intermediates assembled via highly convergent/divergent routes to afford docosahexaenoic (DHA), eicosapentaenoic (EPA), arachidonic, linolenic, and linoleic acids all labeled with carbon-13 at every odd-numbered position. The synthesis may also lead to an economical method to produce pure DHA and EPA for research and therapeutic usage where a high purity is necessary.